Orthodontic treatment involves movement of malpositioned teeth to desired locations in the oral cavity. One common type of orthodontic treatment involves the use of small, slotted orthodontic appliances known as brackets. The brackets are fixed to the patient's teeth and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of teeth to desired locations. The ends of orthodontic archwires are often connected to small orthodontic appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the patient's upper and lower dental arches. The brackets, buccal tubes and archwires are commonly collectively referred to as “braces”.
Orthodontic appliances that are adapted to be adhesively bonded to the patient's teeth can be placed and fixed to the teeth using, for example, one of two techniques known as direct bonding and indirect bonding.
In general, direct bonding techniques involve the serial placement of individual adhesive-coated orthodontic appliances, such as brackets, onto a patient's tooth surface by an orthodontist. Typically, one bracket at a time is placed onto a patient's tooth surface until all of the brackets required for treatment are placed on the teeth. Orthodontic brackets can be manufactured with a layer or coating of orthodontic adhesive on the base of each bracket. Alternatively, a layer or coating of orthodontic adhesive can be applied to the base of each bracket by the orthodontist immediately before the bracket is placed onto a tooth surface. In direct orthodontic bonding, the layer or coating of orthodontic adhesive on the appliance is not hardened until after the appliance is placed on a tooth surface. The layer or coating of orthodontic adhesive does not have a contour that is a negative replica of the tooth surface until the adhesive has been placed in contact with the tooth surface. Direct bonding techniques have been used to place and fix a single orthodontic appliance or many orthodontic appliances in a patient's oral cavity.
In general, indirect bonding techniques involve the use of a placement device or transfer apparatus having a shape that matches the configuration of at least part of the patient's dental arch. One type of placement device includes a “transfer tray” and typically has a cavity for receiving a number of teeth simultaneously. A set of orthodontic appliances such as brackets are releasably connected to (for example, embedded in) the tray at certain, predetermined locations. When the tray with embedded orthodontic appliances is placed over the matching portions of the patient's dental arch, each appliance is ultimately positioned on the patient's teeth at the proper location.
Before the tray is formed, the orthodontic appliances are fixed to replica teeth of a model (typically a “stone model”) of the patient's dental arch. Typically, an orthodontic adhesive is applied to the orthodontic brackets, the brackets are pressed onto the replica teeth, and the orthodontic adhesive is fully hardened using, for example, an orthodontic curing light. This fully hardened orthodontic adhesive can remain on the orthodontic appliance when it is removed from the replica teeth and can serve as a “custom base” for bonding the appliances to the patient's teeth.
With indirect bonding techniques, the transfer apparatus helps to locate the appliances in their proper, intended positions so that individual adjustment of each appliance on the surface of the tooth before bonding is unnecessary. The placement accuracy of the orthodontic appliances that is often afforded by indirect bonding techniques helps ensure that the patient's teeth are moved to their proper, intended positions by the conclusion of orthodontic treatment.